X-ray crystallographic studies of proteins have proved to be most rewarding in obtaining unparalleled detailed structural information about proteins. In addition, the protein crystals have provided the "ideal solid-state experimental systems for studying interactive binding" between enzymes and inhibitors, enzymes and substrate analogues, enzymes and cofactors, etc. Now a similar line of research can be launched with nucleic acids since the first nucleic acid tertiary structure, the three dimensional structure of yeast phenylalanine transfer RNA, has just been determined by the X-ray crystallographic method. This tRNA crystal can now be considered as a solid-state experimental system for studying binding between nucleic acid and interacting molecules. The objectives of the proposed research are structural studies on the interactive binding complexes between RNA and basic peptides, RNA and RNA, RNA and DNA, RNA and aromatic carcinogens, RNA and aromatic mutagens, RNA and antibiotics, RNA and dye molecules, using yeast phenylalanine tRNA crystaals as a solid state experimental system model compound for RNA. The major experimental technique will be the X-ray crystallographic method.